  We study the four-genus of linear combinations of torus knots: aT(p,q) #
-bT(p',q'). Fixing positive p, q, p', and q', our focus is on the behavior of
the four-genus as a function of positive a and b. Three types of examples are
presented: in the first, for all a and b the four-genus is completely
determined by the Tristram-Levine signature function; for the second, the
recently defined Upsilon function of Ozsvath-Stipsicz-Szabo determines the
four-genus for all a and b; for the third, a surprising interplay between
signatures and Upsilon appears.
