Trading losses (cap on income tax relief)

Could someone please explain section 1.2 of this text for me with clear example: 1.1 if loss relief is claimed against total income the maximum that can be relieved is the higher of: a) 50,000 b)25% of person's total income (after deducting gross personal pension contributions) 1.2 this restriction does not apply to the loss relieved against profits of the same trade for the preceding tax year. Thank you so much in advance