Page 416 - Makino,Tsutusi.DictionaryOfIntermediateJGrammar

In. Vmasu + ppoi can be replaced by Vinf .nonpast + yasui as in [5], but
depending on the verb with which -ppoi is connected, the -yasui ver-
sion becomes marginal, as shown in [6].
btL IIILL
[5] a. $LIi@2ilrT&%B~ {7W< /Fb<l 7277k
(These days I became tired easily.)

[6] a. Ebi%~2=T~b%b {7E< /??Pb<l h7k0
(My father has become short tempered since he became
old.)

(+ rashii (DBJG. 373-75); -yasui (DBJG. 541-43); ydda (DBJG: 547-52))