A vivid parallel is available in Ahmes' shorthand. In RMP 31 and RMP 36, two rational numbers 28/97 and 30/53 were not converted in unit fraction series in their present forms. Ahmes applied a 2/n table rule,
letting n/p = 2/p + (n -2)/p
to achieve a fast conversion to unit fraction series, the 2/n table method was adapted by Fibonacci into subtraction context by apparently using only 1/p, as mentioned in Fibonacci's 4th distinction:
20/53 = 19/53 + 1/53
with (19/53 - 1/3) = (3+ 1)/159 = 1/53 + 1/159
Ahmes' 2850 year older arithmetic considered the aliquot parts of 56, and 4 for 28/97 and 30 and 2 for 30/53 and writing:
Summary: Sigler offered no proof that an algorithm was used by Fibonacci. The best way to explain Fibonacci's seventh distinction is to clarify a Medieval context for solving 28/97 and 30/97 examples, thereby drawing a numerical parallel to Ahmes' method. Fibonacci fairly concluded that his seventh conversion method works for all examples, a fact that is attested during by Ahmes by applying a modified 2/n table rule reported in RMP 31 and RMP 36.