4) The last term of 4)F = AB '+BC' D+AC' D+C' D '+ABC' d'+ABC' moves forward and is absorbed by 1, 2 terms.

=AB'+BC'D + C'D'+ABC '

=A(B'+BC')+C'(BD+D') A+A'B=A+B

=A(B'+C')+C'(D'+B)

=AB'+AC'+C'D'+BC '

=(AB'+BC'+AC') +C'D' AC' is absorbed.

=AB'+C'D'+BC '