( ii) that the injury, loss or damage was caused by or contributed to
by an act or omission,
( iii) that the act or omission was that of the person against whom
the claim is made, and
( iv) that, having regard to the nature of the injury, loss or dam-
age, a proceeding would be an appropriate means to seek to
remedy it; and
(b) the day on which a reasonable person with the abilities and in the
circumstances of the person with the claim first ought to have
known of the matters referred to in clause (a).
(2) A person with a claim shall be presumed to have known of the matters
referred to in clause (1)(a) on the day the act or omission on which the claim
is based took place, unless the contrary is proved.
. . . . .
Ultimate limitation periods
15(1) Even if the limitation period established by any other section of this
Act in respect of a claim has not expired, no proceeding shall be commenced
in respect of the claim after the expiry of a limitation period established by
(2) No proceeding shall be commenced in respect of any claim after the 15th
anniversary of the day on which the act or omission on which the claim is
based took place.
. . . . .
Contribution and indemnity
18(1) For the purposes of subsection 5(2) and section 15, in the case of
a claim by one alleged wrongdoer against another for contribution and
indemnity, the day on which the first alleged wrongdoer was served with the
claim in respect of which contribution and indemnity is sought shall be
deemed to be the day the act or omission on which that alleged wrongdoer’s
claim is based took place.
 Certain important features of these provisions bear emphasis.
 First, s. 4 establishes the basic limitation period, which is
two years following the “discovery” of a claim. This is followed by
s. 5, which sets out the basis for determining the date upon which
a claim is “discovered”. As s. 5(1) indicates, a claim can be discovered in one of two ways: either the person with the claim actually
discovers the four matters specified in s. 5(1)(a), or a person
“with the abilities and in the circumstances of the person” ought
to have discovered those four matters.
 The date for determining the discovery of a claim is further
clarified by s. 5(2), which provides that, for purposes of s. 5(1)(a),