set W2 = W .remove (m,n);
A1: len (W .remove (m,n)) <= len W by Lm26;
now :: thesis: W .remove (m,n) is Trail-like
per cases ( ( m is odd & n is odd & m <= n & n <= len W & W . m = W . n ) or not m is odd or not n is odd or not m <= n or not n <= len W or not W . m = W . n ) ;
suppose A2: ( m is odd & n is odd & m <= n & n <= len W & W . m = W . n ) ; :: thesis: W .remove (m,n) is Trail-like
then reconsider m9 = m, n9 = n as odd Element of NAT ;
now :: thesis: for a, b being even Element of NAT holds
( not 1 <= a or not a < b or not b <= len (W .remove (m,n)) or not (W .remove (m,n)) . a = (W .remove (m,n)) . b )
given a, b being even Element of NAT such that A3: 1 <= a and
A4: a < b and
A5: b <= len (W .remove (m,n)) and
A6: (W .remove (m,n)) . a = (W .remove (m,n)) . b ; :: thesis: contradiction
1 <= b by ;
then A7: b in dom (W .remove (m,n)) by ;
a <= len (W .remove (m,n)) by ;
then A8: a in dom (W .remove (m,n)) by ;
now :: thesis: contradiction
per cases ( a in Seg m or ( m <= a & a <= len (W .remove (m,n)) ) ) by A2, A8, Lm34;
suppose a in Seg m ; :: thesis: contradiction
then A9: (W .remove (m,n)) . a = W . a by ;
now :: thesis: contradiction
per cases ( b in Seg m or ( m <= b & b <= len (W .remove (m,n)) ) ) by A2, A7, Lm34;
suppose A10: b in Seg m ; :: thesis: contradiction
A11: b <= len W by ;
(W .remove (m,n)) . b = W . b by ;
hence contradiction by A3, A4, A6, A9, A11, Lm57; :: thesis: verum
end;
suppose A12: ( m <= b & b <= len (W .remove (m,n)) ) ; :: thesis: contradiction
then reconsider b2 = (b - m9) + n9 as even Element of NAT by ;
A13: b2 <= len W by ;
A14: (W .remove (m,n)) . b = W . b2 by ;
now :: thesis: contradiction
per cases ( a < b2 or b2 <= a ) ;
suppose A15: b2 <= a ; :: thesis: contradiction
A16: n - m >= m - m by ;
A17: a - b < b - b by ;
((n - m) + b) - b <= a - b by ;
then 0 <= a - b by A16;
hence contradiction by A17; :: thesis: verum
end;
end;
end;
hence contradiction ; :: thesis: verum
end;
end;
end;
hence contradiction ; :: thesis: verum
end;
suppose A18: ( m <= a & a <= len (W .remove (m,n)) ) ; :: thesis: contradiction
then reconsider a2 = (a - m9) + n9 as even Element of NAT by ;
reconsider nm4 = n9 - m9 as even Element of NAT by ;
A19: (W .remove (m,n)) . a = W . a2 by ;
now :: thesis: contradiction
per cases ( b in Seg m or ( m <= b & b <= len (W .remove (m,n)) ) ) by A2, A7, Lm34;
suppose A20: ( m <= b & b <= len (W .remove (m,n)) ) ; :: thesis: contradiction
then reconsider b2 = (b - m9) + n9 as even Element of NAT by ;
A21: b2 <= len W by ;
A22: (W .remove (m,n)) . b = W . b2 by ;
now :: thesis: contradiction
per cases ( a2 < b2 or b2 <= a2 ) ;
end;
end;
hence contradiction ; :: thesis: verum
end;
end;
end;
hence contradiction ; :: thesis: verum
end;
end;
end;
hence contradiction ; :: thesis: verum
end;
hence W .remove (m,n) is Trail-like by Lm57; :: thesis: verum
end;
suppose ( not m is odd or not n is odd or not m <= n or not n <= len W or not W . m = W . n ) ; :: thesis: W .remove (m,n) is Trail-like
hence W .remove (m,n) is Trail-like by Def12; :: thesis: verum
end;
end;
end;
hence W .remove (m,n) is Trail-like ; :: thesis: verum