USA Are both SEP-IRA + 401K are allowed from the same employer in the same year

[ISA]

S-Corp (with owner / solo employee) has 401K and SEP-IRA
Are contributions to both SEP-IRA + 401K allowed from the same employer in the same year (to the owner / solo employee)?
If yes, what are the limitations and IRS publication spelling it out?

Is it correct, that S-Corp contributions to a 401K are limited and deductible on S-Corp return only up to 25% of employee's compensation?