theorem Th94: for a be positive Nat holds
  b,c are_coprime & a+1 divides b implies not a+1 divides c
  proof
    let a be positive Nat;
    assume
    A1: b,c are_coprime & a+1 divides b;
    A2: a+1 > 0+1 by XREAL_1:6;
    assume not thesis;
    hence contradiction by A1,A2,PYTHTRIP:def 1;
  end;
