What are correct ways to represent relational operators in MathML?

Relational operators should be represented according to "ISO 80000-2 Quantities and Units - Mathematics" specifications. Here are some examples:

Equal-To - The Equal-To relational operation states that both operands represent the same value or object. The operator should be expressed with the Equal symbol = (U+003D or =). For example:

<math><msup><mi>a</mi><mn>2</mn></msup><mo>-</mo>
  <msup><mi>b</mi><mn>2</mn></msup><mo>=</mo>
  <mo>(</mo><mi>a</mi><mo>+</mo><mi>b</mi><mo>)</mo>
  <mo>(</mo><mi>a</mi><mo>-</mo><mi>b</mi><mo>)</mo></math>
    $a^2-b^2=(a+b)(a-b)$

Equal by Definition - The Equal-by-Definition relational operation states that the first operand is explicitly defined to be equal to the second operand. The operator should be expressed with the Equal by Definition symbol: ≝ (U+225D or ≝). For example:

<math><mi mathvariant="normal">i</mi><mo>&#x225D;</mo>
  <msqrt><mn>-1</mn></msqrt></math>
    $\mathrm{i}\stackrel{\scriptscriptstyle\mathrm{def}}{=}\sqrt{-1}$

Other Relational Operators - Some other relational operators are:

• < (U+003C or &#x003C;) for less-than.
• ≤ (U+2264 or &#x2264;) for less-than-or-equal-to.
• > (U+003E or &#x003e;) for greater-than.
• ≥ (U+2265 or &#x2265;) for greater-than-or-equal-to.
• ≠ (U+2260, &#x2260; or &ne;) for not-equal.

⇒ Logical Values and Operator Symbols

⇐ Arithmetic Operator Symbols

⇑ ISO 80000-2 Quantities and Units - Mathematics

⇑⇑ MathML (Mathematical Markup Language)