介
=
人
+
丿
+
丨
:
Mnemonic symbol: 介 looks like a rocket 🚀. Neanderthal Man (人) and Joan of Arc (ji) are preparing a rocket (介) for its start. Between (介) the layers of the outer shell (介) they are stuffing bananas (丿) and dinosaur bones (丨).
(of time or place) in; at; on / (indicating any indirect relation) to; toward; vis-à-vis; with regard to; for / (indicating a source) from; out of / (used in comparison) than / (used in the passive voice) by
于
=
亅
+
二
:
Mnemonic symbol: prepositions (in, at, on, to, ...) are what glue the sentence together. Honey is as sticky as glue, so I'll represent 于 by a honey jar.
Yu the Great (于) was assigned to repair the electronics of the space station's kitchen (Ø2), but instead he was snacking honey from a honey jar (于). Unfortunately his capacitor (二) got stuck in the honey and now he has to use a crowbar (亅) to lever it out.