diff --git a/src/matchers.jl b/src/matchers.jl
index 7f4dea53..e5ace3a1 100644
--- a/src/matchers.jl
+++ b/src/matchers.jl
@@ -5,29 +5,67 @@
 # 2. Dictionary
 # 3. Callback: takes arguments Dictionary × Number of elements matched
 #
+
 function matcher(val::Any)
-    iscall(val) && return term_matcher(val)
+    # if val is a call (like an operation) creates a term matcher or term matcher with defslot
+    if iscall(val)
+        # if has two arguments and one of them is a DefSlot, create a term matcher with defslot
+        # just two arguments bc defslot is only supported with operations with two args: *, ^, +
+        if length(arguments(val)) == 2 && any(x -> isa(x, DefSlot), arguments(val))
+            return defslot_term_matcher_constructor(val)
+        # else return a normal term matcher
+        else
+            return term_matcher_constructor(val)
+        end
+    end
+
     function literal_matcher(next, data, bindings)
+        # car data is the first element of data
         islist(data) && isequal(car(data), val) ? next(bindings, 1) : nothing
     end
 end
 
 function matcher(slot::Slot)
     function slot_matcher(next, data, bindings)
-        !islist(data) && return
+        !islist(data) && return nothing
         val = get(bindings, slot.name, nothing)
+        # if slot name already is in bindings, check if it matches
         if val !== nothing
             if isequal(val, car(data))
                 return next(bindings, 1)
             end
-        else
-            if slot.predicate(car(data))
-                next(assoc(bindings, slot.name, car(data)), 1)
+        # elseif the first element of data matches the slot predicate, add it to bindings and call next
+        elseif slot.predicate(car(data))
+            next(assoc(bindings, slot.name, car(data)), 1)
+        end
+    end
+end
+
+function opposite_sign_matcher(slot::Slot)
+    function slot_matcher(next, data, bindings)
+        !islist(data) && return nothing
+        val = get(bindings, slot.name, nothing)
+        if val !== nothing
+            if isequal(val, car(data))
+                return next(bindings, 1)
             end
+        elseif slot.predicate(car(data))
+            next(assoc(bindings, slot.name, -car(data)), 1) # this - is the only differenct wrt matcher(slot::Slot)
         end
     end
 end
 
+function opposite_sign_matcher(defslot::DefSlot)
+    opposite_sign_matcher(Slot(defslot.name, defslot.predicate))
+end
+
+# this is called only when defslot_term_matcher finds the operation and tries
+# to match it, so no default value used. So the same function as slot_matcher
+# can be used
+function matcher(defslot::DefSlot)
+    matcher(Slot(defslot.name, defslot.predicate))
+end
+
 # returns n == offset, 0 if failed
 function trymatchexpr(data, value, n)
     if !islist(value)
@@ -84,12 +122,12 @@ function matcher(segment::Segment)
     end
 end
 
-function term_matcher(term)
+function term_matcher_constructor(term)
     matchers = (matcher(operation(term)), map(matcher, arguments(term))...,)
-    function term_matcher(success, data, bindings)
 
-        !islist(data) && return nothing
-        !iscall(car(data)) && return nothing
+    function term_matcher(success, data, bindings)
+        !islist(data) && return nothing # if data is not a list, return nothing
+        !iscall(car(data)) && return nothing # if first element is not a call, return nothing
 
         function loop(term, bindings′, matchers′) # Get it to compile faster
             if !islist(matchers′)
@@ -101,8 +139,123 @@ function term_matcher(term)
             car(matchers′)(term, bindings′) do b, n
                 loop(drop_n(term, n), b, cdr(matchers′))
             end
+            # explenation of above 3 lines:
+            # car(matchers′)(b,n -> loop(drop_n(term, n), b, cdr(matchers′)), term, bindings′)
+            #                <------ next(b,n) ---------------------------->
+            # car = first element of list, cdr = rest of the list, drop_n = drop first n elements of list
+            # Calls the first matcher, with the "next" function being loop again but with n terms dropepd from term
+            # Term is a linked list (a list and a index). drop n advances the index. when the index sorpasses
+            # the length of the list, is considered empty
         end
 
-        loop(car(data), bindings, matchers) # Try to eat exactly one term
+        result = loop(car(data), bindings, matchers)
+        # if data is of the alternative form 1/(...)^(...), it might match with negative exponent
+        if operation(term)==^
+            alternative_form = (operation(car(data))==/) && arguments(car(data))[1]==1 && iscall(arguments(car(data))[2]) && (operation(arguments(car(data))[2])==^)
+            if result === nothing && alternative_form
+                denominator = arguments(car(data))[2]
+                # let's say data = a^b with a and b can be whatever
+                # if b is not a number then call the loop function with a^-b
+                if !isa(arguments(denominator)[2], Number)
+                    frankestein = arguments(denominator)[1] ^ -(arguments(denominator)[2])
+                    result = loop(frankestein, bindings, matchers)
+                else
+                    # if b is a number, like 3, we cant call loop with a^-3 bc it
+                    # will automatically transform into 1/a^3. Therfore we need to
+                    # create a matcher that flips the sign of the exponent. I created
+                    # this matecher just for `Slot`s and not for terms, because if b
+                    # is a number and not a call, certainly doesn't match a term (I hope).
+                    if isa(arguments(term)[2], Slot)
+                        matchers2 = (matcher(operation(term)), matcher(arguments(term)[1]), opposite_sign_matcher(arguments(term)[2])) # is this ok to be here or should it be outside neg_pow_term_matcher?
+                        result = loop(denominator, bindings, matchers2)
+                    end
+                end
+            end
+        end
+        result
+    end
+end
+
+# creates a matcher for a term containing a defslot, such as:
+# (~x + ...complicated pattern...)     *          ~!y
+#    normal part (can bee a tree)   operation     defslot part
+
+# defslot_term_matcher works like this:
+# checks wether data is a call.
+#     if yes (1): continues like term_matcher (if it finds a match returns (2))
+#     if still no match found checks wether data (is just a symbol) or (is a tree not starting with the default operation) 
+#          if no returns nothing, rule is not applied
+#          if yes (3): adds the pair (default value name, default value) to the found bindings and 
+#          calls the success function like term_matcher would do
+
+function defslot_term_matcher_constructor(term)
+    a = arguments(term) # lenght two bc defslot term matcher is allowed only with +,* and ^, that accept two arguments
+    matchers = (matcher(operation(term)), map(matcher, a)...) # create matchers for the operation and the two arguments of the term
+    
+    defslot_index = findfirst(x -> isa(x, DefSlot), a) # find the defslot in the term
+    defslot = a[defslot_index]
+    
+    function defslot_term_matcher(success, data, bindings)
+        # if data is not a list, return nothing
+        !islist(data) && return nothing
+        result = nothing
+        if iscall(car(data))
+            # (1)
+            function loop(term, bindings′, matchers′) # Get it to compile faster
+                if !islist(matchers′)
+                    if  !islist(term)
+                        return success(bindings′, 1)
+                    end
+                    return nothing
+                end
+                car(matchers′)(term, bindings′) do b, n
+                    loop(drop_n(term, n), b, cdr(matchers′))
+                end
+            end
+
+            result = loop(car(data), bindings, matchers) # Try to eat exactly one term
+            # if data is of the alternative form 1/(...)^(...), it might match with negative exponent
+            if operation(term)==^
+                alternative_form = (operation(car(data))==/) && arguments(car(data))[1]==1 && iscall(arguments(car(data))[2]) && (operation(arguments(car(data))[2])==^)
+                if result === nothing && alternative_form
+                    denominator = arguments(car(data))[2]
+                    # let's say data = a^b with a and b can be whatever
+                    # if b is not a number then call the loop function with a^-b
+                    if !isa(arguments(denominator)[2], Number)
+                        frankestein = arguments(denominator)[1] ^ -(arguments(denominator)[2])
+                        result = loop(frankestein, bindings, matchers)
+                    else
+                        # if b is a number, like 3, we cant call loop with a^-3 bc it
+                        # will automatically transform into 1/a^3. Therfore we need to
+                        # create a matcher that flips the sign of the exponent. I created
+                        # this matecher just for `DefSlot`s and not for terms, because if b
+                        # is a number and not a call, certainly doesn't match a term (I hope).
+                        if isa(arguments(term)[2], DefSlot)
+                            matchers2 = (matcher(operation(term)), matcher(arguments(term)[1]), opposite_sign_matcher(arguments(term)[2])) # is this ok to be here or should it be outside neg_pow_term_matcher?
+                            result = loop(denominator, bindings, matchers2)
+                        end
+                    end
+                end
+            end
+            # (2)
+            if result !== nothing
+                return result
+            end
+        end
+        
+        # if data (is not a tree and is just a symbol) or (is a tree not starting with the default operation)
+        if ( !iscall(car(data)) || (iscall(car(data)) && nameof(operation(car(data))) != defslot.operation) )
+            other_part_matcher = matchers[defslot_index==2 ? 2 : 3] # find the matcher of the normal part
+            
+            # checks wether it matches the normal part
+            #                             <-----------------(3)------------------------------->
+            bindings = other_part_matcher((b,n) -> assoc(b, defslot.name, defslot.defaultValue), data, bindings)
+            
+            if bindings === nothing
+                return nothing
+            end
+            result = success(bindings, 1)
+        end
+        result
     end
 end
diff --git a/src/rule.jl b/src/rule.jl
index 5de0aa79..d20598b2 100644
--- a/src/rule.jl
+++ b/src/rule.jl
@@ -1,7 +1,7 @@
 
 @inline alwaystrue(x) = true
 
-# Matcher patterns with Slot and Segment
+# Matcher patterns with Slot, DefSlot and Segment
 
 # matches one term
 # syntax:  ~x
@@ -16,6 +16,79 @@ Base.isequal(s1::Slot, s2::Slot) = s1.name == s2.name
 
 Base.show(io::IO, s::Slot) = (print(io, "~"); print(io, s.name))
 
+# for when the slot is a symbol, like `~x`
+makeslot(s::Symbol, keys) = (push!(keys, s); Slot(s))
+
+# for when the slot is an expression, like `~x::predicate`
+function makeslot(s::Expr, keys)
+    if !(s.head == :(::))
+        error("Syntax for specifying a slot is ~x::\$predicate, where predicate is a boolean function")
+    end
+
+    name = s.args[1]
+
+    push!(keys, name)
+    :(Slot($(QuoteNode(name)), $(esc(s.args[2]))))
+end
+
+
+
+
+
+
+# matches one term with built in default value.
+# syntax: ~!x
+# Example usage:
+# (~!x + ~y) can match (a + b) but also just "a" and x takes default value of zero.
+# (~!x)*(~y) can match a*b but also just "a", and x takes default value of one.
+# (~x + ~y)^(~!z) can match (a + b)^c but also just "a + b", and z takes default value of one.
+# only these three operations are supported for default values.
+
+struct DefSlot{P, O}
+    name::Symbol
+    predicate::P
+    operation::O
+    defaultValue::Real
+end
+
+# operation | default
+# + | 0
+# * | 1
+# ^ | 1
+function defaultValOfCall(call)
+    if call == :+
+        return 0
+    elseif call == :*
+        return 1
+    elseif call == :^
+        return 1
+    end
+    # else no default value for this call
+    error("You can use default slots only with +, * and ^, but you tried with: $call")
+end
+
+DefSlot(s) = DefSlot(s, alwaystrue, nothing, 0)
+Base.isequal(s1::DefSlot, s2::DefSlot) = s1.name == s2.name
+Base.show(io::IO, s::DefSlot) = (print(io, "~!"); print(io, s.name))
+
+makeDefSlot(s::Symbol, keys, op) = (push!(keys, s); DefSlot(s, alwaystrue, op, defaultValOfCall(op)))
+
+function makeDefSlot(s::Expr, keys, op)
+    if !(s.head == :(::))
+        error("Syntax for specifying a default slot is ~!x::\$predicate, where predicate is a boolean function")
+    end
+
+    name = s.args[1]
+
+    push!(keys, name)
+    tmp = defaultValOfCall(op)
+    :(DefSlot($(QuoteNode(name)), $(esc(s.args[2])), $(esc(op))), $(esc(tmp)))
+end
+
+
+
+
+
 # matches zero or more terms
 # syntax: ~~x
 struct Segment{F}
@@ -37,37 +110,29 @@ function makesegment(s::Expr, keys)
     end
 
     name = s.args[1]
-
+    
     push!(keys, name)
     :(Segment($(QuoteNode(name)), $(esc(s.args[2]))))
 end
 
-makeslot(s::Symbol, keys) = (push!(keys, s); Slot(s))
-
-function makeslot(s::Expr, keys)
-    if !(s.head == :(::))
-        error("Syntax for specifying a slot is ~x::\$predicate, where predicate is a boolean function")
-    end
-
-    name = s.args[1]
-
-    push!(keys, name)
-    :(Slot($(QuoteNode(name)), $(esc(s.args[2]))))
-end
-
-function makepattern(expr, keys)
+# parent call is needed to know which default value to give if any default slots are present
+function makepattern(expr, keys, parentCall=nothing)
     if expr isa Expr
         if expr.head === :call
             if expr.args[1] === :(~)
                 if expr.args[2] isa Expr && expr.args[2].args[1] == :(~)
                     # matches ~~x::predicate
                     makesegment(expr.args[2].args[2], keys)
+                elseif expr.args[2] isa Expr && expr.args[2].args[1] == :(!)
+                    # matches ~!x::predicate
+                    makeDefSlot(expr.args[2].args[2], keys, parentCall)
                 else
                     # matches ~x::predicate
                     makeslot(expr.args[2], keys)
                 end
             else
-                :(term($(map(x->makepattern(x, keys), expr.args)...); type=Any))
+                # make a pattern for every argument of the expr.
+                :(term($(map(x->makepattern(x, keys, operation(expr)), expr.args)...); type=Any))
             end
         elseif expr.head === :ref
             :(term(getindex, $(map(x->makepattern(x, keys), expr.args)...); type=Any))
diff --git a/test/rewrite.jl b/test/rewrite.jl
index c2e920f9..3cd545f2 100644
--- a/test/rewrite.jl
+++ b/test/rewrite.jl
@@ -47,6 +47,58 @@ end
     @eqtest @rule(+(~~x,~y,~~x) => (~~x, ~y, ~~x))(term(+,6,type=Any)) == ([], 6, [])
 end
 
+@testset "Slot matcher with default value" begin
+    r_sum = @rule (~x + ~!y)^2 => ~y
+    @test r_sum((a + b)^2) === b
+    @test r_sum(b^2) === 0
+
+    r_mult = @rule ~x * ~!y  => ~y
+    @test r_mult(a * b) === b
+    @test r_mult(a) === 1
+
+    r_mult2 = @rule (~x * ~!y + ~z) => ~y
+    @test r_mult2(c + a*b) === b
+    @test r_mult2(c + b) === 1
+
+    # here the "normal part" in the defslot_term_matcher is not a symbol but a tree
+    r_mult3 = @rule (~!x)*(~y + ~z) => ~x
+    @test r_mult3(a*(c+2)) === a
+    @test r_mult3(2*(c+2)) === 2
+    @test r_mult3(c+2) === 1
+    
+    r_pow = @rule (~x)^(~!m) => ~m
+    @test r_pow(a^(b+1)) === b+1
+    @test r_pow(a) === 1
+    @test r_pow(a+1) === 1
+
+    # here the "normal part" in the defslot_term_matcher is not a symbol but a tree
+    r_pow2 = @rule (~x + ~y)^(~!m) => ~m
+    @test r_pow2((a+b)^c) === c
+    @test r_pow2(a+b) === 1
+
+    r_mix = @rule (~x + (~y)*(~!c))^(~!m) => ~m + ~c
+    @test r_mix((a + b*c)^2) === (2, c)
+    @test r_mix((a + b*c)) === (1, c)
+    @test r_mix((a + b)) === (1, 1)
+end
+
+@testset "1/power matches power with exponent of opposite sign" begin
+    r1 = @rule (~x)^(~y) => (~x, ~y) # rule with slot as exponent
+    @test r1(1/a^b) === (a, -b) # uses frankestein
+    @test r1(1/a^(b+2c)) === (a, -b-2c) # uses frankestein
+    @test r1(1/a^2) === (a, -2) # uses opposite_sign_matcher
+
+    r2 = @rule (~x)^(~y + ~z) => (~x, ~y, ~z) # rule with term as exponent
+    @test r2(1/a^(b+2c)) === (a, -b, -2c) # uses frankestein
+    @test r2(1/a^3) === nothing # should use a term_matcher that flips the sign, but is not implemented
+
+    r1defslot = @rule (~x)^(~!y) => (~x, ~y) # rule with slot as exponent
+    @test r1defslot(1/a^b) === (a, -b) # uses frankestein
+    @test r1defslot(1/a^(b+2c)) === (a, -b-2c) # uses frankestein
+    @test r1defslot(1/a^2) === (a, -2) # uses opposite_sign_matcher
+    @test r1defslot(a) === (a, 1)
+end
+
 using SymbolicUtils: @capture
 
 @testset "Capture form" begin