predicates
  transform(integer)

clauses
  transform(X) :- X >= 1000, write("M"),  Y=X-1000,  transform(Y).
  transform(X) :- X >=  900, write("CM"), Y=X-900,   transform(Y).
  transform(X) :- X >=  500, write("D"),  Y=X - 500, transform(Y).
  transform(X) :- X >=  400, write("CD"), Y=X-400,   transform(Y).
  transform(X) :- X >=  100, write("C"),  Y=X-100,   transform(Y).
  transform(X) :- X >=   50, write("L"),  Y=X-50,    transform(Y).
  transform(X) :- X >=   40, write("XL"), Y=X-40,    transform(Y).
  transform(X) :- X >    9, write("X"),  Y=X-10,    transform(Y).
  transform(X) :- X =    9, write("IX"), nl.
  transform(X) :- X >    4, write("V"),  Y=X-5,     transform(Y).
  transform(X) :- X =    4, write("IV"),nl.
  transform(X) :- X >=   1, write("I"),  Y=X-1,     transform(Y).
  transform(X) :- X =    0, nl.
  transform(X) :- X <    0, write("-"), Y=-X, transform(Y).

goal
   transform(75).