This is my first post on this SE so I apologize if my formatting is bad.
Essentially I am trying to reproduce the small black symbol from the following definition in Allen Hatcher's Algebraic Topology:
(This book can also be accessed from his website for free, and this particular image is from page 26.)
I am trying to figure out how to typeset the small black square between the f and the g(s). I tried the following in my preamble
but the square bullet produced looks jarring and does not look like a binary operator, i.e. it is not centered and does not have equal spacing between f and g(s).
Would any of you have any suggestions on how to make this particular symbol?