Analysis of information sources in references of the Wikipedia article "Nabla symbol" in English language version.
I took the liberty of asking Professor Ball two days ago whether he had a name for this symbol ∇2, and he has mentioned to me nabla, a humorous suggestion of Maxwell's. It is the name of an Egyptian harp, which was of that shape. I do not know that it is a bad name for it. Laplacian I do not like for several reasons both historical and phonetic. [Jan. 22 1892. Since 1884 I have found nothing better, and I now call it Laplacian.]As this is written, he appears to be naming the Laplacian ∇2 "nabla", but in the lecture was presumably referring to ∇ itself.
Here, the brackets and superscript fs together serve to denote fictitiousness; thus the nabla says "It is indeterminate whether", and the rest says "a=b (fictively)."We can represent cases of this form, cases where it is indeterminate whether in fiction f: a=b, as follows:
(A) ∇[f a = b]f.
