diff --git a/polimani.pl b/polimani.pl
index eedd134..bca9745 100644
--- a/polimani.pl
+++ b/polimani.pl
@@ -2,11 +2,17 @@
 %% Follows 'Coding guidelines for Prolog' - Theory and Practice of Logic Programming
 %% https://doi.org/10.1017/S1471068411000391
 
+%% Import the Constraint Logic Programming over Finite Domains lybrary
+%% Essentially, this library improves the way Prolog deals with integers,
+%% allowing more predicates to be reversible.
+%% For instance, number(N) is always false, which prevents the
+%% reversing of a predicate.
+:- use_module(library(clpfd)).
+
 %% polynomial_variable_list(-List:atom) is det
 %
 %  List of possible polynomial variables
 %
-
 polynomial_variable_list([x, y, z]).
 
 %% polynomial_variable(?X:atom) is det
@@ -16,37 +22,73 @@ polynomial_variable_list([x, y, z]).
 polynomial_variable(X) :-
     polynomial_variable_list(V),
     member(X, V).
-polynomial_variable(P) :-
-    polynomial_variable_list(V),
-    member(X, V),
-    P = X^_.
+%% polynomial_variable(P) :-
+%%     polynomial_variable_list(V),
+%%     member(X, V),
+%%     P = X^N,
+%%     N == 1.
 %% Tests:
 %% ?- polynomial_variable(x).
 %@ true .
+%% ?- polynomial_variable(x^(1)).
+%@ false.
 
-%% power(+X:atom) is det
+%% power(+X:atom) is semidet
 %
 %  Returns true if X is a power term, false otherwise.
+%  Fully reversible.
 %
-power(X ^ N) :-
-    %% X ^ N = P,
-    integer(N),
-    !,
-    %% write(N),
-    N >= 1,
-    polynomial_variable(X),
-    !.
+power(P^N) :-
+    %% CPL(FD) library predicate to perform integer comparassions in a reversible way
+    %% If 0 > N succeds, fail, otherwise check if X is a valid variable
+    (zcompare((<), 0, N), polynomial_variable(P)); fail.
+    %% if(zcompare((>), 0, N),
+    %%    fail,
+    %%    polynomial_variable(X)
+    %% ).
 power(X) :-
-    polynomial_variable(X),
-    !.
+    polynomial_variable(X).
 %% Tests:
+%% ?- power(x).
+%@ true .
 %% ?- power(x^1).
 %@ true .
+%% ?- power(x^3).
+%@ false.
+%@ false.
+%@ false.
+%@ true .
+%@ true .
 %% ?- power(x^(-3)).
 %@ false.
-%@ true.
-%@ -3
+%@ false.
 %@ true .
+%@ false.
+%@ true .
+%@ false.
+%% ?- power(X).
+%@ X = x ;
+%@ X = y ;
+%@ X = z.
+
+%% if(+P, -T, -F) is det
+%
+%  A simple implementation of an if predicate.
+%  Returns T if P is true
+%  or F if P otherwise
+%
+%% if(If_1, Then_0, Else_0) :-
+%%     call(If_1, T),
+%%     (  T == true -> call(Then_0)
+%%     ;  T == false -> call(Else_0)
+%%     ;  nonvar(T) -> throw(error(type_error(boolean,T),_))
+%%     ;  /* var(T) */ throw(error(instantiation_error,_))
+%%     ).
+if(P, T, F) :- (P == true, T); F.
+%% ?- if(true, N = 1, N = 2).
+%@ N = 1 .
+%% ?- if(false, N = 1, N = 2).
+%@ N = 2.
 
 %% term(+N:atom) is det
 %
@@ -63,6 +105,8 @@ term(L * R) :-
 %% ?- term(2*x^3).
 %@ true .
 %% ?- term(x^(-3)).
+%@ false.
+%% ?- term((-3)*x^2).
 %@ true .
 
 %% is_term_valid_in_predicate(+T, +F) is det
@@ -95,22 +139,37 @@ polynomial(L + R) :-
     polynomial(L),
     term(R).
 %% Tests:
-%% TODO
+%% ?- polynomial(x).
+%@ true .
+%% ?- polynomial(x^3).
+%@ true .
+%% ?- polynomial(3*x^7).
+%@ true .
+%% ?- polynomial(2 + 3*x + 4*x*y^3).
+%@ true .
 
 %% power_to_canon(+T:atom, -T^N:atom) is det
 %
 %  Returns a canon power term.
 %
 power_to_canon(T^N, T^N) :-
-    polynomial_variable(T).
+    polynomial_variable(T),
+    %% N \= 1.
+    (
+	zcompare(=, 1, N)
+    ;
+	true
+    ).
 power_to_canon(T, T^1) :-
     polynomial_variable(T).
 %% Tests:
 %% ?- power_to_canon(x, X).
-%@ X = x^1.
-%% ?- power_to_canon(X, X^1).
+%@ X = x^1 .
+%% ?- power_to_canon(X, x^1).
 %@ X = x .
-%@ X = x.
+%@ X = x .
+%% ?- power_to_canon(X, x^4).
+%@ X = x^4 .
 
 %% term_to_list(?T, ?List) is det
 %
@@ -132,12 +191,12 @@ term_to_list(P, [P2]) :-
 %% Tests:
 %% ?- term_to_list(1*2*y*z*23*x*y*x^3*x, X).
 %@ X = [x^1, x^3, y^1, x^1, 23, z^1, y^1, 2, 1] .
-%@ X = [x^1, x^3, y^1, x^1, 23, z^1, y^1, 2] .
 %% ?- term_to_list(X, [y^1, x^1]).
 %@ X = x*y .
 %% ?- term_to_list(X, [x^4]).
-%@ X = x^4 .
 %@ false.
+%@ false.
+%@ X = x^4 .
 %% ?- term_to_list(X, [y^6, z^2, x^4]).
 %@ X = x^4*z^2*y^6 .