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IDIJ
IDIJ (Increment Decrement If Jump) is an OISC by User:None1.
There is a tape with infinite cells and every cell is an unbounded signed integer.
The only command is:
A B C D
Increment address A then decrement address B, then if address C is 0, jump to line D (1-indexed).
Computational class
Turing complete, because you can easily compile it from minsky machine. Let's use 2-register minsky machine as an example:
Let N be current line number:
Increment register A:
0 2 0 N
Increment register B:
1 2 0 N
If register A is 0, jump to somewhere, otherwise decrement register A:
2 2 0 position 2 0 0 N
If register B is 0, jump to somewhere, otherwise decrement register B:
2 2 1 position 2 1 0 N
Translation for minsky machines with more than two registers can be made using similar techniques.