for a, b, c being Element of TarskiEuclid2Space st ex jj being Real st
( 0 <= jj & jj <= 1 & (Tn2TR b) - (Tn2TR a) = jj * ((Tn2TR c) - (Tn2TR a)) ) holds
Tn2TR b in LSeg ((Tn2TR a),(Tn2TR c))