Is there an add-on or extension that I should install to correctly display mathematical symbols on Writer? My teacher sends me docx files with logic formulas using symbols like the material implication (→), the material equivalence (↔), the logical negation (¬), logical conjunction/disjunction and so on, however they don’t display correctly.
What is your operating system name/version and LibreOffice version? What do you see instead of “don’t display correctly” characters? Do you see some other characters for each of character or do you see square (sign for non existing character font) or something else?
Word uses special font called “Symbols” which contains these (or probably something else). Such usage is strongly discouraged after inventing of Unicode. However for you to see these correctly you need to install that font on your computer as well. To see the name of the font just place your cursor to one of these symbols and look at the font name dropdown.
To be clear, it is OK to use a font to display symbols (LO uses the OpenSymbol font for the same purpose), so long as the symbols are encoded in the correct Unicode code point. Problems become apparent when existing code points are re-purposed within a font. The Unicode Private Use Area (U+E000…U+F8FF), Supplemental Private Use Area-A (U+F0000…U+FFFFD), and Supplemental Private Use Area-B (U+100000…U+10FFFD) are specifically set aside for custom uses.