Gordian vs involutional

Gordian

adj

Of or pertaining to Gordius, king of Phrygia
Of the Gordian knot.
Twisted; convoluted; tied as a knot.
Of or pertaining to Gordium (now Yassihüyük in Turkey), capital of Phrygia.

name

Gordianus, name of three Roman emperors.

involutional

adj

of or pertaining to involution
characterized by involution

How often have the words Gordian and involutional occurred in a corpus of books? (source: Google Ngram Viewer )