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Edited to reflect @AliTaghavi's correction
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EDIT: Sorry, I realised after a moment that I was thinking 'realistically'; thisThe map is not good$f \mathrel: \ell \mapsto \ell \oplus \ell'$, sincewhere $\ell' = \ell$$\ell' = \mathbb C\cdot\overline{(b, -a, d, -c)}$ when $\ell = \mathbb C\cdot(1, i, 1, i)$. I tried to delete this answer but could not$\ell = \mathbb C\cdot(a, b, c, d)$, since it has been acceptedsatisfies your first condition.

The map $f \mathrel: \ell \mapsto \ell \oplus \ell'$(I originally had a version without the complex conjugation, wherewhich doesn't work because $\ell' = \mathbb C\cdot(b, -a, d, -c)$$\ell' = \ell$ when $\ell = \mathbb C\cdot(a, b, c, d)$, is$\ell = \mathbb C\cdot(1, i, 1, i)$. Fortunately @AliTaghavi pointed out how to fix it. The candidate without the conjugation would have been holomorphic, and satisfies your first conditionhence contradicted @abx's answer.)

EDIT: Sorry, I realised after a moment that I was thinking 'realistically'; this map is not good, since $\ell' = \ell$ when $\ell = \mathbb C\cdot(1, i, 1, i)$. I tried to delete this answer but could not, since it has been accepted.

The map $f \mathrel: \ell \mapsto \ell \oplus \ell'$, where $\ell' = \mathbb C\cdot(b, -a, d, -c)$ when $\ell = \mathbb C\cdot(a, b, c, d)$, is holomorphic, and satisfies your first condition.

The map $f \mathrel: \ell \mapsto \ell \oplus \ell'$, where $\ell' = \mathbb C\cdot\overline{(b, -a, d, -c)}$ when $\ell = \mathbb C\cdot(a, b, c, d)$, satisfies your first condition.

(I originally had a version without the complex conjugation, which doesn't work because $\ell' = \ell$ when $\ell = \mathbb C\cdot(1, i, 1, i)$. Fortunately @AliTaghavi pointed out how to fix it. The candidate without the conjugation would have been holomorphic, hence contradicted @abx's answer.)

This answer is wrong
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LSpice
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EDIT: Sorry, I realised after a moment that I was thinking 'realistically'; this map is not good, since $\ell' = \ell$ when $\ell = \mathbb C\cdot(1, i, 1, i)$. I tried to delete this answer but could not, since it has been accepted.

The map $f \mathrel: \ell \mapsto \ell \oplus \ell'$, where $\ell' = \mathbb C\cdot(b, -a, d, -c)$ when $\ell = \mathbb C\cdot(a, b, c, d)$, is holomorphic, and satisfies your first condition.

The map $f \mathrel: \ell \mapsto \ell \oplus \ell'$, where $\ell' = \mathbb C\cdot(b, -a, d, -c)$ when $\ell = \mathbb C\cdot(a, b, c, d)$, is holomorphic, and satisfies your first condition.

EDIT: Sorry, I realised after a moment that I was thinking 'realistically'; this map is not good, since $\ell' = \ell$ when $\ell = \mathbb C\cdot(1, i, 1, i)$. I tried to delete this answer but could not, since it has been accepted.

The map $f \mathrel: \ell \mapsto \ell \oplus \ell'$, where $\ell' = \mathbb C\cdot(b, -a, d, -c)$ when $\ell = \mathbb C\cdot(a, b, c, d)$, is holomorphic, and satisfies your first condition.

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LSpice
  • 12.9k
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  • 69

The map $f \mathrel: \ell \mapsto \ell \oplus \ell'$, where $\ell' = \mathbb C\cdot(b, -a, d, -c)$ when $\ell = \mathbb C\cdot(a, b, c, d)$, is holomorphic, and satisfies your first condition.