This volume contains the papers presented at the 4th FMM Workshop affiliated with CICM 2019 that took place on July 8, 2019 in Prague. The workshop series allows mathematicians interested in computer assistance and researchers in formal and computer-understandable mathematics to meet and exchange ideas. The meeting provides a platform for discussion of suitable forms of computer assistance between the formal community and interested mathematicians and other researchers. The workshop started with the invited talk of Chad E. Brown: Higher-Order Logic and Set Theory: Stronger Together. Six contributed papers have been reviewed by at least two program committee members and obtain the average 2.1. The committee decided to accept all papers.