Basically, you look in one person’s account to see if there is enough money to make a transfer, and if there is, you transfer the money. I’ll bet you’ve done that before.

In fact, here’s the whole program:

10 LET account1 = 200.00
20 LET account3 = 300.00
30 INPUT “Value to exchange for transaction”; exchange
40 IF account1 < exchange THEN PRINT “Inadequate value”: STOP
50 account1 = account1 – exchange
60 account3 = account3 + exchange
70 PRINT “Instruction to 1st institution: adjust 2nd account by ”; -exchange

This implementation demonstrates that Alice’s patented invention requires only seven simple lines of code, not complex programming or specially designed hardware.

via A Patent on Seven Simple Lines of Code – Public Knowledge.