Bug 136974

Description:
The math / formula editor currently allows a range of arrows, including double arrows point right (drarrow), left (dlarrow), or left-and-right (dlrarrow). 

However, no such arrows pointing up and/or down are defined in the manual (Math Guide  version 6.4). These arrows are quite standard in mathematics, so they would be natural to include.

Also missing: An arrow for reversible chemical reactions, i.e. two arrows above each other, the upper pointing left, the lower pointing right. This has been asked for in at least two questions on the forum:
https://ask.libreoffice.org/en/question/60428/formula-double-arrows-for-chemical-equations/
https://ask.libreoffice.org/en/question/160395/double-harpoon-arrow-for-type-chemistry/
Even though the answers to the questions indicate workarounds, it is a standard chemical symbol that (IMHO) would be a natural addition to the equation editor - as well as the symbols menu.

Steps to Reproduce:
1. Open formula editor
2. Look through subgroups to find these symbols

Actual Results:
In subgroup "Relations", the left/right double arrows are defined, but not up/down. Through the Functions > Symbols > Edit menu, double up (Ux21D1) and double down (Ux21D3) can be found, but not the combination up&down. The chemical reversible arrow set cannot be found. 

Expected Results:
These symbols should be part of the implemented symbols. Suggested naming:

duarrow: double up-arrow (corresponding to Ux21D1)
ddarrow: double down-arrow (corresponding to Ux21D3)
dudarrow: double up-and-down arrow
loverrarrow: chemical left-over-right arrow for reversible reactions


Reproducible: Always


User Profile Reset: No



Additional Info:
Version: 7.0.1.2 (x64)
Build ID: 7cbcfc562f6eb6708b5ff7d7397325de9e764452
CPU threads: 8; OS: Windows 10.0 Build 19041; UI render: Skia/Vulkan; VCL: win
Locale: da-DK (da_DK); UI: da-DK
Calc: threaded