  We explain the construction of Forcer, a FORM program for the reduction of
four-loop massless propagator-type integrals to master integrals. The resulting
program performs parametric IBP reductions similar to the three-loop Mincer
program. We show how one can solve many systems of IBP identities
parametrically in a computer-assisted manner. Next, we discuss the structure of
the Forcer program, which involves recognizing reduction actions for each
topology, applying symmetries, and transitioning between topologies after edges
have been removed. This part is entirely precomputed and automatically
generated. We give examples of recent applications of Forcer, and study the
performance of the program. Finally we demonstrate how to use the Forcer
package and sketch how to prepare physical diagrams for evaluation by Forcer.
