οὐκ ἂν λάβοις παρὰ τοῦ μὴ ἔχοντος → you can't take from one who doesn't have, you can't squeeze blood out of a turnip, you can't get blood out of a turnip, you can't get blood from a stone, you can't get blood out of a stone
ἰσοπραξία, ἡ (Μ)
ίση, όμοια θέση ή κατάσταση.
[ΕΤΥΜΟΛ. < ἰσ(ο)- + -πραξία (< πράξις), πρβλ. δικαιο-πραξία, ευ-πραξία].