anthem-rs/examples/example-exact-cover.spec

# Auxiliary predicate to determine whether a variable is integer
#axiom: forall X (is_int(X) <-> exists N X = N).

# Perform the proofs under the assumption that n is a nonnegative integer input constant. n stands
# for the total number of input sets
input: n -> integer.
assume: n >= 0.

# s/2 is the input predicate defining the sets for which the program searches for exact covers
input: s/2.

# Only the in/1 predicate is an actual output, s/2 is an input and covered/1 and is_int/1 are
# auxiliary
output: in/1.

# Perform the proofs under the assumption that the second parameter of s/2 (the number of the set)
# is always an integer
assume: forall Y (exists X s(X, Y) -> exists N (Y = N and N >= 1 and N <= n)).

# Only valid sets can be included in the solution
spec: forall Y (in(Y) -> exists N (Y = N and N >= 1 and N <= n)).
# If an element is contained in an input set, it must be covered by all solutions
spec: forall X (exists Y s(X, Y) -> exists Y (in(Y) and s(X, Y))).
# Elements may not be covered by two input sets
spec: forall Y, Z (exists X (s(X, Y) and s(X, Z)) and in(Y) and in(Z) -> Y = Z).