Using Permute to Sort (Inefficiently)

sorted( [ X ] ) .

sorted( [ A, B | R ] ) :- A = < B ,

sorted( [ B | R ] ) .

sort2( L, S ) :- permute( L, S ), sorted( S ) .

sort2( [ 2, 3, 1 ], Ans )

permute( [ 2, 3, 1 ], Ans )

permute( [ 2, 3, 1 ], [ 2, 3, 1 ] ) sorted( [ 2, 3, 1 ] )

fail

permute( [ 2, 3, 1 ], [ 3, 2, 1 ] ) sorted( [ 3, 1, 2 ] )

fail

permute( [ 2, 3, 1 ], [ 3, 1, 2 ] ) sorted( [ 3, 1, 2 ] )

fail

permute( [ 2, 3, 1 ], [ 1, 2, 3 ] ) sorted( [ 2, 1, 3 ] )

fail

permute( [ 2, 3, 1 ], [ 1, 2, 3 ] ) sorted( [ 1, 2, 3 ] )

Ans = [ 1, 2, 3 ]