thorough knowledge of something

to be well versed in something, to be thoroughly acquainted with something

mathematics (field of study)

he / distal demonstrative, something far off removed from both speaker and listener: that / boyfriend

distal demonstrative, something far off removed from both speaker and listener: that, yon / particularly, male personal third person pronoun: he / by extension from he: boyfriend

he; boyfriend

(mathematics) discrete mathematics

applied mathematics

(mathematics) pure mathematics

mathematician