The half-pitch (HP) is defined by the Rayleigh Resolution Equation. The smallest HP that can be printed in single exposure is 36 nm. However, a k1 process factor of 0.25 is considered to be a very difficult, if not impossible, process. Today's best processes have k1 = 0.28. So, the practical half pitch is about 38 - 40 nm.
Here is a slide from IMEC that shows the (practical) limits of various multiple patterning techniques:
45nm 193i LE3 (used by Samsung N10 process)
40nm 193i SADP (used by Intel and TSMC N10 processes)
28nm EUV single exposure (See Toshiba slide for explanation)
20nm 193i SAQP