theorem Satz5p2:
  a <> b & between a,b,c & between a,b,d implies between b,c,d or between b,d,c
  proof
    assume
A1: a <> b & between a,b,c & between a,b,d;
    then between a,c,d or between a,d,c by Satz5p1;
    hence thesis by A1,Satz3p6p1;
  end;
