Formulate the sequencing constraints for the above conditions.

Variables:

The presence of either$$or constraints poses a problem since the model is no

longer of the linear programming $($LP$)$ format $($i$.$e$.,$ the either$$or constraint

creates a nonconvex solution space$).$ This difficulty is overcome by introducing the binary variables YAB defined by

YAB $1$ if task A preceeds task B

$0$ if task B preceeds task A

Constraint:

A transformation of the either$$or constraints, discussed above, is required

as follows:

XA $$ dA XB $$ M$(1$ YAB$)$