Maps with shared keys. about vim-arpeggio HOT 1 OPEN

Thank you for the report. As you described, such mappings (one is a subset of the other) basically doesn't work because of conflict. Internally,

• the first one maps t and h to recognize whether two keys (t and h) are simultaneously pressed, and
• the second one maps t, h and a to recognize whether three keys (t, h and a) are simultaneously pressed.

The point is that the second one overrides t and h, so that the example doesn't work.
(If the second one consists of two keys (like Arpeggio inoremap ta ...), it doesn't conflict with the first one.)

As a workaround, reorder mappings by lhs length. For example,

Arpeggio inoremap tha that
Arpeggio inoremap th the

from vim-arpeggio.