Since, it is given that AB=CE, CD=EF.
To Prove: AB = DF
Proof:
CD = EF (Given)
CD+DE = DE+EF (Addition property of Equality)
CE = CD+DE (Segment Addition)
DF = DE+EF
Since, CE = CD+DE and CD+DE = DE+EF and DE+EF = DF
So, CE = DF(Transitive Property of Equality)
Transitive property of Equality states that "If a = b and b = c, then a = c".