+ + +
Solvent
Catalyst

In this reaction, carried out in liquid ammonia, the KOH abstracts a proton from the acetylene, forming the acetylide anion, which nucleophilically attacks the acetone.

Industrial Organic Chemistry, 3rd. Ed. K. Weissermel, H.-J. Arpe, VCH (1997)

Reaction defined as:
Addition: Nucleophilic
Industrial Process: Organic