let n1, n2, n3, n4 be Element of NAT ; :: thesis: for S being Gene-Set
for p1, p2 being Individual of S holds
( ( n1 >= len p1 implies crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n2,n3,n4) ) & ( n2 >= len p1 implies crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n1,n3,n4) ) & ( n3 >= len p1 implies crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n1,n2,n4) ) & ( n4 >= len p1 implies crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n1,n2,n3) ) )

let S be Gene-Set; :: thesis: for p1, p2 being Individual of S holds
( ( n1 >= len p1 implies crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n2,n3,n4) ) & ( n2 >= len p1 implies crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n1,n3,n4) ) & ( n3 >= len p1 implies crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n1,n2,n4) ) & ( n4 >= len p1 implies crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n1,n2,n3) ) )

let p1, p2 be Individual of S; :: thesis: ( ( n1 >= len p1 implies crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n2,n3,n4) ) & ( n2 >= len p1 implies crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n1,n3,n4) ) & ( n3 >= len p1 implies crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n1,n2,n4) ) & ( n4 >= len p1 implies crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n1,n2,n3) ) )
A1: ( n4 >= len p1 implies crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n1,n2,n3) )
proof
assume n4 >= len p1 ; :: thesis: crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n1,n2,n3)
then n4 >= len S by Def1;
then A2: n4 >= len (crossover (p1,p2,n1,n2,n3)) by Def1;
crossover (p1,p2,n1,n2,n3,n4) = crossover ((crossover (p1,p2,n1,n2,n3)),(crossover (p2,p1,n1,n2,n3)),n4) ;
hence crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n1,n2,n3) by A2, Th5; :: thesis: verum
end;
A3: ( n2 >= len p1 implies crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n1,n3,n4) )
proof
assume A4: n2 >= len p1 ; :: thesis: crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n1,n3,n4)
then n2 >= len S by Def1;
then A5: n2 >= len p2 by Def1;
crossover (p1,p2,n1,n2,n3,n4) = crossover ((crossover (p1,p2,n1,n3)),(crossover (p2,p1,n1,n2,n3)),n4) by A4, Th19
.= crossover ((crossover (p1,p2,n1,n3)),(crossover (p2,p1,n1,n3)),n4) by A5, Th19 ;
hence crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n1,n3,n4) ; :: thesis: verum
end;
A6: ( n3 >= len p1 implies crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n1,n2,n4) )
proof
assume A7: n3 >= len p1 ; :: thesis: crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n1,n2,n4)
then n3 >= len S by Def1;
then A8: n3 >= len p2 by Def1;
crossover (p1,p2,n1,n2,n3,n4) = crossover ((crossover (p1,p2,n1,n2)),(crossover (p2,p1,n1,n2,n3)),n4) by A7, Th20
.= crossover ((crossover (p1,p2,n1,n2)),(crossover (p2,p1,n1,n2)),n4) by A8, Th20 ;
hence crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n1,n2,n4) ; :: thesis: verum
end;
( n1 >= len p1 implies crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n2,n3,n4) )
proof
assume A9: n1 >= len p1 ; :: thesis: crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n2,n3,n4)
then n1 >= len S by Def1;
then A10: n1 >= len p2 by Def1;
crossover (p1,p2,n1,n2,n3,n4) = crossover ((crossover (p1,p2,n2,n3)),(crossover (p2,p1,n1,n2,n3)),n4) by A9, Th18
.= crossover ((crossover (p1,p2,n2,n3)),(crossover (p2,p1,n2,n3)),n4) by A10, Th18 ;
hence crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n2,n3,n4) ; :: thesis: verum
end;
hence ( ( n1 >= len p1 implies crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n2,n3,n4) ) & ( n2 >= len p1 implies crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n1,n3,n4) ) & ( n3 >= len p1 implies crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n1,n2,n4) ) & ( n4 >= len p1 implies crossover (p1,p2,n1,n2,n3,n4) = crossover (p1,p2,n1,n2,n3) ) ) by A3, A6, A1; :: thesis: verum