Therefore, esomark-chan is a furby. Q.E.D.

Therefore, esomark-chan is a furby. Q.E.D. is an "esoteric programming language" by user:raiseafloppafan7741 in 2026.

Overview

The program is a string of "esomark-chan"s and "furby"s which correspond to 1s and 0s in a binary number with the MSB at the leftmost position respectively. For example, the number "41" (101001 in binary) would be:

esomark-chan furby esomark-chan furby furby esomark-chan

The number is then factored to its prime numbers which are then sorted in ascending order. The prime factor list is then run in a loop forever, with the only way to halt being via making the factor list empty.

Prime factor	Action
2	Swaps the next two factors. Wrapping.
3	Multiplies the next two factors and replaces them with the sorted factors of their product.
5	Squares the next factor and factorizes the square.
7	Takes the rounded-down integer square root of the next factor and replaces it with that.
11	Reverses the execution direction.
13	Squares all prime factors in the prime factor list, factorizes each of the squares, sorts the factors of the squares individually, concatenates the lists, replaces the current factor list, and sets the execution pointer to the first element. For example, [2, 5, 3] will square to [4, 25, 9] which factorize into [[2, 2], [5, 5], [3, 3]] which results in the new factor list [2, 2, 5, 5, 3, 3].
17	Skips the next factor after this one.
19	Sums the 8 prime factors after it (wrapping) and replaces them with the sum.
23	Multiplies the 9 prime factors after it (wrapping) and replaces them with the product.
29	Copies the next factor and moves the copy to the end of the factor list.
31	Copies the previous factor and moves the copy to the end of the factor list.
37	Clones the entire factor list and appends the clone to the end.
41	If the next prime factor's square is odd, then the next prime factor is skipped.
43	If the next prime factor's square is even, then the next prime factor is skipped.
47	If the next prime factor's square is a semiprime, then the next prime factor is skipped.
53	Removes the next prime factor.
59	Removes the previous prime factor.
61	Multiplies all of the current factors, factors the product, replaces the current factor list with the ascending sorted factor list of the product, and puts the execution pointer at the first factor.
67	No-op.
71	Replaces the next factor with the ascending sorted factors of 3x + 1 where x is the next factor.
73	Replaces the next prime factor with the prime number that comes before it, with 2 being replaced with 2. For example, 73 71 results in 73 67.
79	Replaces the next prime factor with the prime number that comes after it. For example, 73 61 results in 73 67.
83	If the next factor is a duplicate of the previous factor, the next factor is removed.
89	If the previous factor is a duplicate of the next factor, the previous factor is removed.
97	Takes the next two prime factors A and B and replaces both of them with the sorted factors of A mod B.
101	Take the next factor P, remove P from the factor list, let N be P's index, for example 2's index is 1, 3's index is 2, 5's index is 3, and so on. Remove the next N factors.
103	Take the next factor P, remove P from the factor list, let N be P's index, for example 2's index is 1, 3's index is 2, 5's index is 3, and so on. Remove the previous N factors.
107	Take the next factor P, remove P from the factor list, let N be P's index, for example 2's index is 1, 3's index is 2, 5's index is 3, and so on. Skips them.
109	Take the next factor K and the factor after that P P, remove K and P from the factor list, let N be P's index, for example 2's index is 1, 3's index is 2, 5's index is 3, and so on. Perform K's operation for each of the following N primes in order after the 109 after the deletion.
113	Insert after it the greatest (in value) last deleted prime factor.

Prime factors not in the above table will be run through the steps of the Collatz conjecture until they reach a prime number factor that is in the table.