Perpetual futures

A perpetual never expires; a periodic funding payment tethers it to an index. With a positive rate longs pay shorts. The BitMEX-style rate clamps the premium against an interest term:

$F=P+\operatorname{clamp}(I-P,\,-c,\,+c)$

Liquidation is judged against a manipulation-resistant mark price, not the last trade. The concept traces to Shiller's (1993) perpetual claim.

Code: mechanisms/perp.py · Demo: examples/sim_perp.py