Invitation to negotiate.

$7/2/2020$: ColbyCo sends Mathis Holdings a letter expressing an interest in

purchasing the Tar Sands. ColbyCo asks Mathis to name your price.

$7/3/2020$: Denver$-$Carrington sends Mathis Holdings a bid to purchase the Tar

Sands oil field for $$12$ billion.

$7/4/2020$: Denver$-$Carrington reconsiders and sends Mathis Holdings a letter

retracting the $$12$ billion bid and lowering it to $$10$ billion.

$7/5/2020$: Mathis receives ColbyCo's $7/2/2020$ letter.

$7/5/2020$: Mathis sends ColbyCo an offer to sell the Tar Sands for $$15$ billion.

No one at Mathis expects ColbyCo to take the offer, and everyone expects the

Tar Sands to sell at around $$8$ billion.

$7/6/2020$: Mathis receives Denver$-$Carrington's $7/3/2020$ $$12$ billion bid and

immediately sends a letter of acceptance.

$7/6/2020$: Mathis sends ColbyCo a retraction of its $$15$ billion offer.

$7/7/2020$: Mathis receives Denver$-$Carrington's $7/4/2020$ $$10$ billion bid.

$7/7/2020$: ColbyCo receives Mathis' $7/5/2020$ $$15$ billion offer and sends an

A timeline of events is given below. Match these events with their significance: Has an offer been

made? Has a contract been formed? Has anything legally significant happened at all?