What are correct ways to represent arithmetic operators in MathML?

"ISO 80000-2 Quantities and Units - Mathematics" specifies that arithmetic operators should be represented as described below:

Addition - The addition operator should be expressed with the "Plus" symbol: + (U+002B or +), which is the ASCII "+" character. For example: a + b.

Subtraction - The subtraction operator should be expressed with the "Minus" symbol: − (U-2212, − or &#minus;), which is not the same as the ASCII "-" character. For example: a − b.

Note that negative values should also be expressed with the "Minus" symbol without trailing space. For example: −b.

Multiplication - The multiplication operator should be expressed with 3 options:

• Multiplication symbol: : (U-00D7 or × or ×), which is not the same as the ASCII "x" character.
• Dot Operator symbol: ⋅ (U-22C5 or &#22C5; or ·), which is not the same as the ASCII "." character.
• Implied Multiplication: No operator symbol between two operands with no space or a thin space. In this case, the Invisible Times character, U-2062 (ࠎ or ⁢), can be used.

Note that obelus asterisk, * (U+002A or *), is commonly used programming languages as the multiplication operator. But it is not recommended by the ISO 80000-2 standard.

Division - The multiplication operator should be expressed with 2 options:

• Forward Slash: / (U+002F or /). For example: a / b.
• Fraction Bar: A solid horizontal line to separate the numerator and the denominator vertically as $\frac{a}{b}$. This should be constructed with the <mfrac> element.

Note that division symbol, ÷ (U+00F7 or &#x00F7;), and the obelus symbol, ⁒ (U+2052 or &#x2052;), are commonly used programming languages as division operators. But they are not recommended by the ISO 80000-2 standard.

⇒ Relational Operator Symbols

⇐ Function Arguments - U+2061 and "mrow" Tag

⇑ ISO 80000-2 Quantities and Units - Mathematics

⇑⇑ MathML (Mathematical Markup Language)