With no explanation, label text_A→text_B with either "DON'T KNOW", "NO" or "YES".
text_A: A real number "a" is first-order definable in the language of set theory, without parameters, if there is a formula "φ" in the language of set theory, with one free variable, such that "a" is the unique real number such that "φ"("a") holds (see). This notion cannot be expressed as a formula in the language of set theory.
text_B: Would a reader who had only a basic college-level introduction to mathematics be able to read this passage and conclude that a skilled mathematician could "solve for a," so to speak, given the way the notion can ostensibly be expressed?
NO.