# LaggedLink

From OpenCog

The LaggedLink is a predicate transformer that takes a temporal predicate and shifts it in the past, or possibly in the future if the lag is negative. It is used to define the PLN semantics of SequentialAndLink and such.

## Format

LaggedLink P T

where P is a temporal predicate and T is a time difference (maybe represented by a TimeNode, although we may want to introduce a TimeDifferenceNode).

## Semantics

Assuming for now a temporal predicate with two arguments

P(x, t)

where x is atemporal, and t represents time, then

LaggedLink P T

is equivalent to

LambdaLink x, t P(x, t-T)

## Example

Let us define the temporal predicate

tall(p, t)

representing if person p is tall, perhaps to some degree, at time t.

Then

(Lagged tall 1y)(John, Now)

represents the tallness of John a year ago. While

(Lagged tall -1y)(Mary, Now)

represents the tallness of Mary a year from now. And

(Lagged tall 1d)(Eva, Tomorrow)

represents the tallness of Eva now.